When the server finishes starting, show "Jellyfin started successfully" with a
5-second "Redirecting in N…" countdown and a Cancel button instead of reloading
immediately. Cancel stops the countdown and the background refresh so the
startup output can be reviewed, and offers a "Continue to Jellyfin" button to
reload manually. The buttons use the web client's emby-button styling.
Also drop the transitional "Applying migrations" activity: it only showed
briefly while the pending migration set was read, or for the whole step when
nothing was pending, so startup now goes from "Preparing migrations" straight
into "Running migration X of Y".
Restyle the startup/migration holding page to match the Jellyfin dark theme,
with the inline wordmark logo, a gradient spinner and a recolored startup log
tree, and move the Morestachio template rendering into a reusable
StartupUiRenderer.
Add a curated, non-identifying "current activity" line to the always-visible
header (for example "Initializing server" or "Running migration X of Y"),
reported from the startup flow and the migration service so it never leaks
server details to unauthenticated clients. Move the log download into a
"Download logs" link in the log panel header, and show only the header, with
no log hints, to non-local clients.
